1. Field of the Invention
The present invention relates to a voltage converting circuit and a radio communication apparatus, and, more particularly is suitably applied to a method of converting a common potential of a differential signal.
2. Description of the Related Art
In a circuit on which a digital circuit and an analog circuit are mixed, in some case, a signal treated by the analog circuit is differentiated to prevent deterioration in the quality of an analog signal due to digital noise.
When circuit blocks having different DC levels are directly coupled to each other, the circuit blocks do not normally operate. Therefore, in general, a capacitor is interposed between the circuit blocks to interrupt a DC component.
For example, Japanese Patent Application Laid-Open No. 2002-76800 discloses a method of increasing a sum of electric currents flowing to a pair of transistors in proportion to an input differential voltage to realize linear subtraction and addition functions over a wide input voltage range. Gates of the transistors form an input pair, drains thereof form a subtraction output pair, and sources thereof are connected in common to form an addition output terminal.
However, in the method of interposing the capacitor between the circuit blocks, bands up to near the DC component are interrupted. Therefore, the method cannot be applied to, for example, a communication system that needs to allow the bands up to near the DC component to pass.
In the method disclosed in Japanese Patent Application Laid-Open No. 2002-76800, a differential signal is converted into a single-phase signal by a differential circuit on an output side and a common potential generated by the input pair is cancelled. Therefore, it is impossible to adjust a common potential of the differential signal while allowing the differential signal to be transmitted.